This application claims priority to an application entitled xe2x80x9cMethod and Device For Spreading and Modulation to Reduce Peak-to-Average Power Ratio of Mobile Transmit Powerxe2x80x9d filed in the Korean Industrial Property Office on May 12, 1998 and assigned Serial No. 98-17046, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to mobile communication systems, and in particular, to a device and method for reducing the peak-to-average power ratio of a mobile station""s transmit power in a mobile communication system.
2. Description of the Related Art
A typical CDMA mobile communication system focuses on voice service, whereas a 3G mobile communication system provides the additional services of high quality voice, high speed data, moving pictures, and Internet browsing. In such a mobile communication system, a radio link consists of a forward link directed from a base station (BS) to a mobile station (MS) and a reverse link directed from the MS to the BS.
When zero-crossing occurs during spreading and modulation in a reverse link transmission (a phase variation is xcfx80), the peak-to-average power ratio of the mobile station""s transmit power (mobile transmit power) increases, thereby producing regrowth. Regrowth adversely affects the communication quality of calls being made by other subscribers. Hence, the peak-to-average power ratio is a significant factor in the design and performance of a power amplifier in an MS.
Regrowth occurs due the existence of a linear portion and a non-linear portion in a characteristic curve of the mobile station""s power amplifier. As the mobile transmit power increases, a transmit signal of the MS due to the non-linear characteristics generates interference in the frequency area of a different user causing the regrowth phenomenon.
Regrowth can be prevented by shrinking down a cell and sending a signal from an MS in the cell to a corresponding BS at a low power level. Thus, mobile transmit power can be flexibly controlled if the mobile station""s peak-to-average power ratio can be limited to a specific range. However, it is not economical to physically shrink a cell, since more cells are then needed for a given area and each cell requires its own communications equipment.
Accordingly, an object of the present invention is to provide device and method for reducing the peak-to-average power ratio of a mobile station""s transmit power in a mobile communication system.
Another object of the present invention is to provide a method of flexibly controlling mobile transmit power by limiting its peak-to-average power ratio to a specific range.
A further object of the present invention is to provide a method of flexibly varying a cell size in a mobile communication system to counteract regrowth.
A still further object of the present invention is to provide a method of enhancing auto-correlation characteristics of a multipath signal and cross-correlation characteristics relative to other users.
To achieve these and other objects, a device and method for reducing the peak-to-average power ratio of mobile transmit power in a mobile communication system are provided. The device and method spread mobile transmission data by a complex spreading sequence. The complex spreading sequence includes a plurality of chips and is generated to have a phase difference of 90xc2x0 between every two successive complex chips in response to each chip of a PN (Pseudo Noise) sequence.